1. Field of the Invention
This invention generally relates to a pattern recognition method and system, and, in particular, to a character recognition method and system for recognizing unknown, input characters by comparing with registered, known characters. More specifically, the present invention relates to a character subdividing method suitable for use in a character recognition method and system. Furthermore, the present invention relates to a character recognition method using a multi-layer directionality code histogram technique.
2. Description of the Prior Art
A character recognition method including a step of subdividing a character pattern into a plurality of mesh regions and a step of collectively processing feature quantities of the character pattern for each of the mesh regions is well known. However, in the case where subdividing points for subdividing the character pattern into mesh regions, it is prone to deformations of a character pattern so that the rate of recognition using fixed subdividing points for such characters as hand-written kanji (Chinese) characters tends to be significantly deteriorated. In order to prevent the rate of recognition from being deteriorated by deformations of character patterns, there has been proposed a character pattern subdividing method using variable subdividing points as disclosed, for example, in the Japanese Patent Application No. 59-202823 assigned to the assignee of this application. In accordance with this method using variable subdividing points, the subdividing points for subdividing a character pattern into mesh regions are variably determined such that predetermined feature quantities of the character pattern are equally distributed among the subdivided mesh regions.
Furthermore, there is another Japanese Patent Application No. 59-202825 which has also been assigned to the assignee of this application and which discloses a character recognition method employing such a variable character pattern subdividing method and collectively processing the feature quantities of the character pattern for each of the subdivided mesh regions. With this variable character pattern subdividing method, the rate of character recognition can be less affected by modifications of character patterns as compared with the fixed subdividing method, so that there is obtained an increased rate of recognition for hand-written characters or the like. However, with the above-described character pattern recognition method, the adjacent subdivided mesh regions do not overlap each other or even if they do overlap, an overlapping width remains constant. As a result, depending on the manner and degree of deformations of a character pattern, there is a case in which the fluctuations of feature quantities due to deformations of a character pattern cannot be absorbed sufficiently.